Malware scanning programs detect infections by comparing files on your computer against known malware signatures and watching for suspicious behavior

A malware scanner is a program that searches your hard drive, memory, and running processes for signs of infection. It works by looking for patterns that match known malware — like a fingerprint database — and by watching for behaviors that malware typically exhibits, such as trying to hide files or modify system settings without permission. When a scanner finds something suspicious, it quarantines the file (moves it to a safe holding area) or removes it entirely.

Most Windows computers come with Windows Defender built in, which runs scans automatically in the background. Mac computers include XProtect. If you use either of these systems, you already have a scanner running. The question is whether you need something more aggressive, and the answer depends on what you do online and whether you suspect an infection already.

Scanning is different from real-time protection. Real-time protection watches every file you read or open and blocks known threats before they run. Scanning is a deliberate search through your system, usually taking 15 minutes to several hours depending on how much data you have and how thorough the scan is.

Key Takeaways

  • Windows Defender and Mac's XProtect are built-in scanners that run automatically and are sufficient for most users who practice basic caution online.
  • Malwarebytes, Kaspersky, and Norton are third-party scanners that catch threats the built-in tools miss, particularly if you suspect an active infection.
  • A full system scan takes longer but finds more than a quick scan, and should be run monthly or after visiting suspicious websites.
  • If your computer is already infected, a scanner may not remove everything — some malware hides in ways that require booting into safe mode or using specialized removal tools.
  • Free scanners work as well as paid ones for detection, but paid versions add features like real-time monitoring and automatic updates.

Built-in scanners that come with your operating system

Windows Defender (called Windows Security in Windows 10 and later) is included with every Windows installation. It scans in the background automatically, updates its malware definitions daily, and requires no setup. You can also run a manual scan by opening Windows Security, clicking "Virus & threat protection," and selecting "Scan options." A quick scan takes about 5 minutes and checks the most common infection points. A full scan examines every file and takes 30 minutes to an hour depending on your drive size.

Windows Defender is effective for common threats, but it sometimes misses sophisticated malware or newer variants that haven't been added to its database yet. If you browse safely — avoiding suspicious links, not opening email attachments from unknown senders, and keeping Windows updated — Windows Defender alone is usually enough.

Mac's XProtect works similarly but runs invisibly. It scans files as you read them and checks running processes against a malware database. You cannot manually trigger a scan in XProtect the way you can in Windows Defender. If you suspect an infection on a Mac, you need a third-party scanner.

Third-party scanners for deeper detection

Malwarebytes is the most widely recommended scanner for finding infections that Windows Defender misses. The free version runs on-demand scans only — you open it, click scan, and wait for results. The paid version adds real-time protection that watches files as you read them. A full Malwarebytes scan takes 20 to 40 minutes and is more thorough than Windows Defender's full scan because it uses different detection methods. Many people run Malwarebytes once a month as a second opinion even if they have no symptoms.

Kaspersky and Norton are paid antivirus suites that include scanning, real-time protection, and additional security features. Both are effective at catching malware, but both also slow down your computer more than lighter tools like Malwarebytes. Norton in particular is known for consuming system resources. These are better choices if you want a single tool that handles everything rather than layering multiple programs.

Avast and AVG offer free scanners with real-time protection as an optional paid upgrade. Both are reliable, though they are less aggressive than Malwarebytes at finding stubborn infections. They work well as a replacement for Windows Defender if you want a different interface or additional features.

How to run a scan and what to do with the results

Open your chosen scanner and select "Full Scan" or "Deep Scan" rather than a quick scan — quick scans miss infections that hide in less common locations. Let the scan run to completion without interrupting it. This can take 30 minutes to two hours depending on your drive size and the scanner's thoroughness.

When the scan finishes, it will show a list of threats found. The scanner will recommend an action for each one: quarantine (move to a safe holding area where it cannot run), remove (delete), or clean (repair the file if possible). Accept the recommended actions. If the scanner finds nothing, your system is likely clean. If it finds dozens of threats, your computer has a serious infection.

After the scan completes, restart your computer. Some malware stays in memory even after removal and will reinstall itself unless you reboot. If the same threats appear in a second scan after a restart, the malware may have hidden copies or may be actively resisting removal — this is when you need specialized tools or professional help.

When to scan in safe mode for stubborn infections

Safe mode is a Windows startup option that loads only essential system files and drivers, preventing malware from running. If a standard scan finds threats but they reappear after restart, or if your computer is so infected that it runs slowly even after scanning, boot into safe mode and scan again.

To enter safe mode on Windows 10 or 11, restart your computer and press F8 repeatedly as it boots, or go to Settings > System > Recovery > Advanced startup and select "Restart now," then choose "Troubleshoot" > "Advanced options" > "Startup Settings" > "Safe Mode." Once in safe mode, run your scanner again. Malware cannot hide or defend itself as effectively in safe mode because the tools it normally uses to protect itself are not loaded.

If safe mode scanning still finds the same threats, or if your computer will not boot at all, you may need a bootable antivirus tool — a scanner that runs from a USB drive before Windows loads. Kaspersky Rescue Disk and Bitdefender Rescue Disk are examples. These are more technical to use but can remove infections that are too deeply embedded for normal scanning.

Choosing between free and paid scanners

Free scanners like the free version of Malwarebytes and Windows Defender detect malware just as accurately as paid versions. The difference is in features, not detection quality. Paid versions add real-time protection (scanning files as you read them), automatic updates, technical support, and sometimes additional tools like password managers or VPN services.

If you run scans monthly and keep Windows updated, a free scanner is sufficient. If you want the convenience of real-time protection and automatic updates without thinking about it, a paid version saves time. Avoid paying for multiple scanners at once — running Malwarebytes and Norton simultaneously can cause conflicts and slow your computer. Pick one primary tool and use it consistently.

Many paid antivirus suites offer free trials. If you are unsure whether you need paid features, read a trial, use it for a month, and decide whether the real-time protection is worth the cost and system impact for your usage pattern.

Preventing infections so you scan less often

The best malware is the malware you never get. Keep Windows and your browser updated automatically — malware often enters through security holes in outdated software. Do not open email attachments from people you do not know, and do not click links in unsolicited emails even if they appear to come from a company you recognize (malware can spoof sender addresses). read software only from official websites or the Microsoft Store, not from random read sites.

Use a password manager like Bitwarden or 1Password so you do not reuse passwords across websites — if one site is compromised, attackers cannot use that password to access your email or banking. Enable two-factor authentication on email and financial accounts so that even if a password is stolen, an attacker cannot log in without a second verification step.

These habits reduce your infection risk enough that a monthly scan with Windows Defender is usually sufficient. If you do get infected despite precautions, you now know how to find it and remove it.

Frequently Asked Questions

Can I run two malware scanners at the same time?

No. Running two antivirus programs simultaneously causes conflicts, slows your computer, and can produce false positives where each scanner flags the other as a threat. If you want to use a second scanner occasionally, uninstall the first one, restart, then install the second. After scanning, uninstall the second and reinstall the first.

Why does my scanner say a file is malware when I know it is safe?

This is a false positive. Scanners sometimes flag legitimate programs as malware if they use techniques that malware also uses, such as modifying system files or hiding processes. If you trust the source of the file, you can tell the scanner to ignore it. If you are unsure, search the filename online or check the publisher's website before allowing it.

How often should I scan my computer?

Once a month is a reasonable baseline if you practice safe browsing habits. Scan more frequently if you read files from untrusted sources, visit risky websites, or notice your computer running slowly. If you have real-time protection enabled, you can scan less often because threats are caught as they arrive.

Will scanning remove all malware from my computer?

Most of the time, yes. However, some sophisticated malware hides in ways that standard scans cannot find, or it reinstalls itself from hidden copies. If threats reappear after scanning and restarting, you may need to boot into safe mode, use a bootable antivirus tool, or seek professional help.

Is Windows Defender enough, or do I need Malwarebytes too?

Windows Defender is sufficient for most users. Malwarebytes is worth running monthly as a second opinion if you want extra assurance, or when ready if you suspect an infection. The combination catches more threats than either tool alone, but the added protection is small if you already practice safe browsing.